1. Field of the Invention
This invention relates to an electrophotographic light-sensitive material. More particularly, it is an electrophotographic light-sensitive material having a composite light-sensitive layer formed by a layer of a charge transporting substance and a layer of a charge producing substance on an electrically conductive support.
2. Description of the Prior Art
Various types of light-sensitive materials have been developed and are used in different electrophotographic reproduction processes. All of them, however, have their own drawbacks. For example, a light-sensitive material having a layer of selenium is low in flexibility and its handling involves quite a bit of difficulty, as selenium is a highly toxic substance. A light-sensitive material having a layer of zinc oxide can only poorly be charged with electricity, shows a high degree of charge attenuation in the dark, and is low in sensitivity. There is also known a light-sensitive material having an organic light-sensitive layer formed by a charge transfer complex composed of polyvinylcarbazole and trinitrofluorenone. This material is also low in sensitivity and the toxicity of trinitrofluorenone presents a difficult problem, too.
A composite or laminated type electrophotographic light-sensitive material has been developed to improve the prior materials as hereinabove described. This type of light-sensitive material is disclosed in, for example, Japanese Patent Publications Nos. 42380/1980 and 34099/1985. It comprises an electrically conductive support 3 having a layer of aluminum 2 deposited on a polyester film 1, a layer 4 of a charge producing substance formed on the aluminum layer 2, and a layer 5 of a charge transporting substance formed on the layer 4, as shown by way of example in FIG. 18.
Examples of the charge transporting substance include p-N,N-dialkylaminobenzaldehyde-N',N'-diphenylhydrazone, particularly p-N,N-diethylaminobenzaldehyde-N',N'-diphenylhydrazone, p-N,N-diphenylaminobenzaldehyde-N'-methyl-N'-phenylhydrazone and p-N-ethyl-N-phenyl-aminobenz-aldehyde-N'-methyl-N'phenylhydrazone. The layer of any such substance and the layer of a charge producing substance are laid on the electrically conductive support. The layer of a charge transporting substance is formed by, for example, dissolving it in an organic solvent to prepare a solution containing a binding resin, which may further contain a plasticizer, etc. as required, applying the solution onto the support or the layer of a charge producing substance, and drying it, whereby a layer having a thickness of, say, 5 to 100 microns is formed.
The charge transporting substance has a decisive bearing on the performance or quality of any electrophotographic light-sensitive material of the type to which this invention pertains. The manufacture of an electrophotographic light-sensitive material having high sensitivity requires the provision of a layer containing a charge transporting substance in a relatively high concentration and therefore the use of a charge transporting substance which is highly compatible with the resin used as a bonding agent. The substance must also be one from which any such layer can be formed easily. Moreover, the charge transporting substance is required to have an appropriately low oxidation potential and a high charge transfer rate, so that the charge which is produced in the layer of the charge producing substance may be effectively injected into the layer of the charge transporting substance. However, organic compounds having a low oxidation potential are generally liable to oxidation and unstable.
None of the known hydrazone derivatives as hereinabove mentioned is always satisfactory in view of the required physical properties which have hereinabove been stated. The use of any such hydrazone derivative still fails to provide any electrophotographic light-sensitive material of high sensitivity. None of any such known compounds is satisfactory in stability, either.